White leaf spot pathogen: Neopseudocercosporella capsellae causes significant damage to many economically important Brassicaceae crops, including oilseed rape through foliar, stem, and pod lesions under cool and wet conditions. A lack of information on critical aspects of the pathogen’s life cycle limits the development of effective control measures. The presence of single-celled spores along with multi-celled conidia on cotyledons inoculated with multi-celled conidia suggested that the multi-celled conidia were able to form single-celled spores on the host surface. This study was designed to demonstrate N. capsellae morphological plasticity, which allows the shift between a yeast-like single-celled phase and the multi-celled hyphal phase. Separate experiments were designed to illustrate the pathogen’s morphological transformation to single-celled yeast phase from multi-celled hyphae or multi-celled macroconidia in-vitro and in-planta. Results confirmed the ability of N. capsellae to switch between two morphologies (septate hyphae and single-celled yeast phase) on a range of artificial culture media (in-vitro) or in-planta on the host surface before infection occurs. The hyphae-to-yeast transformation occurred through the production of two morphologically distinguishable blastospore (blastoconidia) types (meso-blastospores and micro-blastospores), and arthrospores (arthroconidia).
Main conclusion Site-specific changes of photosynthesis, a relatively new concept, can be used to improve the productivity of critical food crops to mitigate the foreseen food crisis.
Photosynthesis in wheat (Triticum aestivum L.) pericarps may contribute appreciably to wheat grain yield. Consequently, we investigated the temporal variation of traits related to photosynthesis and sucrose metabolism in the pericarps and flag leaves of three wheat genotypes, Huandoy, Amurskaja 75 and Greece 25, which are reported to differ in expression of genes related to the C4 pathway in wheat grain. Significant site-specific, genotypic and temporal variation in the maximum carboxylation rate (Vcmax) and maximum rates of electron transport (Jmax) (biological capacity of carbon assimilation) were observed early in ontogeny that dissipated by late grain filling. Although the transcript abundance of rbcS and rbcL in flag leaves was significantly higher than in the pericarps, in line with their photosynthetic prominence, both organ types displayed similar expression patterns among growth stages. The higher N concentrations in the pericarps during grain enlargement suggest increased Rubisco; however, expression of rbcS and rbcL indicated the contrary. From heading to 14 days post-anthesis, wheat pericarps exhibited a strong, positive correlation between biological capacity for carbon assimilation and expression of key genes related to sucrose metabolism (SPS1, SUS1 and SPP1). The strong correlation between spike dry weight and the biological capacity for carbon assimilation along with other findings of this study suggest that metabolic processes in wheat spikes may play a major role in grain filling, total yield and quality.
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